【Hive】條件函數

Hive版本: hive-1.1.0-cdh5.14.2

1. if函數

語法：if(boolean testCondition, T valueTrue, T valueFalseOrNull)
返回值: T
描述：如果testCondition爲true，返回valueTrue，否則返回valueFalseOrNull

0: jdbc:hive2://node03:10000> select if(1=2, 'TrueValue', 'FalseOrNull');
+--------------+--+
|     _c0      |
+--------------+--+
| FalseOrNull  |
+--------------+--+

2. 空值判斷函數：isnull / isnotnull

語法：isnull( a ) / isnotnull( a )
返回值：boolean
描述：isnull：如果a爲空，返回true，否則返回false； isnotnull：如果a不爲空，返回true，否則返回false

0: jdbc:hive2://node03:10000> select isnotnull(1) as col1, isnotnull(null) as col2;
+-------+--------+--+
| col1  |  col2  |
+-------+--------+--+
| true  | false  |
+-------+--------+--+

3. 去空函數: nvl

語法：nvl(T value, T default_value)
返回值: T
描述：如果value爲空，返回default_value,否則返回value

0: jdbc:hive2://node03:10000> select nvl(null, 'defaultValue') as col1, nvl(1, 'defaultValue') as clo2;
+---------------+-------+--+
|     col1      | clo2  |
+---------------+-------+--+
| defaultValue  | 1     |
+---------------+-------+--+

4. 非空查找函數：coalesce

語法: COALESCE(T v1, T v2, …)
返回值: T
描述：返回第一個不爲空的T值，如果都爲空，則返回空

0: jdbc:hive2://node03:10000> select coalesce(null,1,2,3) as col1, coalesce(null,null) as col2;
+-------+-------+--+
| col1  | col2  |
+-------+-------+--+
| 1     | NULL  |
+-------+-------+--+

5. 條件判斷函數: case when

語法：（1）CASE a WHEN b THEN c [WHEN d THEN e]* [ELSE f] END
（2）CASE WHEN a THEN b [WHEN c THEN d]* [ELSE e] END
返回值：T
描述：（1）如果a=b，返回c，如果a=d，返回e，否則返回f；
（2）如果a是true，返回b，如果c爲true，返回d，否則返回e；

0: jdbc:hive2://node03:10000> select case 1 when 1 then 1 when 2 then 2 else null end as col1,
. . . . . . . . . . . . . . > case when 1=1 then 1 else null end as col2;
+-------+-------+--+
| col1  | col2  |
+-------+-------+--+
| 1     | 1     |
+-------+-------+--+

6. 斷言函數: assert_true

語法: assert_true(boolean condition)
返回值：void
描述: 如果condition成立，返回null，不成立則拋出異常

0: jdbc:hive2://node03:10000> select assert_true(2<1);
Error: java.io.IOException: org.apache.hadoop.hive.ql.metadata.HiveException: ASSERT_TRUE(): assertion failed. (state=,code=0)

0: jdbc:hive2://node03:10000> select assert_true(1<2);
+-------+--+
|  _c0  |
+-------+--+
| NULL  |
+-------+--+